To be honest, this is like if you got a new job and then within a couple of weeks you were expected to be at the same level as everyone else. It would be completely unfair on you and it is no different for the new boys.
It takes time to learn in a new environment, especially for the young guys like Sandro that have never lived in the UK. Think about everything that he has to take in; New culture, language, city, house, job, boss, colleagues, weather, increased expectations etc. It might even take him a whole year to get up to scratch. The more the fans support these players, the better chance they will have in succeeding.